1. Field of the Invention
This invention relates to a control method for die cast machines and more particularly to a control method for die cast machines which carry out multi-step injection speed control depending on positions of a plunger of an injection cylinder.
2. Description of the Prior Art
Generally, in die cast machines, hydraulically driven injection cylinders are utilized. An injection plunger of the injection cylinder apparatus is advanced at a low injection speed to start injection of molten metal to mold cavities. If the injection plunger advances up to a predetermined position, the injection plunger is advanced at a high injection speed to achieve high speed injection of molten metal to the mold cavities. The multi-step injection speed control is achieved in this manner. In other cases, the injection plunger is advanced at medium injection speeds between a low speed advancement interval and a high speed advancement interval.
Injection speeds of respective speed steps such as the low injection speed and the high injection speed and speed change-over plunger positions such as the high speed injection starting position have each appropriate value which is determined depending on mold data and casting condition data. The multi-step injection speed control is carried out so as to drive the plunger at this appropriate value.
The injection speeds of the respective speed steps such as the low injection speed and the high injection speed are controlled by means of hydraulic pressure control on the injection cylinder apparatus. Thus, actual injection speeds may be changed due to changes in oil temperature and the speed change-over plunger position may be changed due to a delay in action of a low speed--high speed change-over valve of hydraulic system.
However, because generally the injection speed of the die cast machine is high speed, it is difficult to perform feedback compensating control for the aforementioned multi-step injection speed control. Actually, there have been never seen any die cast machines which perform the multi-step injection speed control in feed-back compensation type.
Thus, conventionally correction of speed change-over plunger positions have been achieved depending on sense of operators. Usually corrections of the injection speeds of respective speed steps have not been performed.